Method to reduce dielectric constant of a porous low-k film

ABSTRACT

Embodiments of the present invention generally relate to methods for lowering the dielectric constant of low-k dielectric films used in semiconductor fabrication. In one embodiment, a method for lowering the dielectric constant (k) of a low-k silicon-containing dielectric film, comprising exposing a porous low-k silicon-containing dielectric film to a hydrofluoric acid solution and subsequently exposing the low-k silicon-containing dielectric film to a silylation agent. The silylation agent reacts with Si—OH functional groups in the porous low-k dielectric film to increase the concentration of carbon in the low-k dielectric film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/671,191, filed Jul. 13, 2012 which is herein incorporated byreference in its entirety.

BACKGROUND

1. Field

Embodiments of the present invention generally relate to methods forlowering the dielectric constant of low-k dielectric films used insemiconductor fabrication.

2. Description of the Related Art

The dielectric constant (k) of dielectric films in semiconductorfabrication is continually decreasing as device scaling continues.Minimizing integration damage on low dielectric constant (low-k) filmsis important to be able to continue decreasing feature sizes. However,as feature sizes shrink, improvement in the resistive capacitance andreliability of dielectric films becomes a serious challenge.

Porous low-k dielectric films including for example, carbon-doped oxides(CDO), experience damage to their bonding structures when exposed tointegration steps such as, but not limited to, polishing, etching,ashing, and cleaning. Dielectric films having a higher k-value may bebetter able to survive subsequent integration steps; however, a lowerk-value is typically desirable in the final film as feature sizesshrink. For example, for a damascene process, a patterned low-kdielectric film is typically filled with copper followed by a chemicalmechanical planarization (CMP) process to planarize the copper film. Adielectric film having a higher k-value would be more mechanicallyrobust and better able to survive the CMP process without significantdamage. Whereas a dielectric film having a lower dielectric constantwould be less mechanically robust and significantly damaged by the CMPprocess.

Thus, a method for lowering the k-value of dielectric films is necessaryto improve efficiency and allow for smaller device sizes.

SUMMARY

Embodiments of the present invention generally relate to methods forlowering the dielectric constant of low-k dielectric films used insemiconductor fabrication. In one embodiment, a method for lowering thedielectric constant (k) of a low-k silicon-containing dielectric film,comprising exposing a porous low-k silicon-containing dielectric film toa hydrofluoric acid solution and subsequently exposing the low-ksilicon-containing dielectric film to a silylation agent.

In another embodiment, a method for lowering the dielectric constant (k)of a low-k silicon-containing dielectric film is provided. The methodcomprises exposing a porous low-k silicon-containing dielectric film toa hydrofluoric acid solution, exposing the low-k silicon-containingdielectric film to a vaporized silylation agent, and exposing the low-kdielectric film to an ultraviolet (UV) cure process.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIGS. 1A-1D illustrate a dielectric film during various stages ofprocessing according to embodiments described herein;

FIG. 2 is a process flow diagram illustrating one method of lowering thek-value of a low-k dielectric film according to embodiments describedherein; and

FIG. 3 is a cross-sectional view of an exemplary processing chamber thatmay be used to practice the embodiments described herein.

To facilitate understanding, identical reference numerals have beenused, wherever possible, to designate identical elements that are commonto the figures. It is contemplated that elements and/or process steps ofone embodiment may be beneficially incorporated in other embodimentswithout additional recitation.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to methods forlowering the dielectric constant of low-k dielectric films used insemiconductor fabrication. VLSI/ULSI demands the use of backenddielectrics with increasingly low dielectric constants. One potentialapplication of the embodiments described herein is to allow a dielectricfilm with a high dielectric constant (i.e., less carbon) to survivecertain integration steps and then be processed to have an increasedcarbon concentration (i.e., lower-k). Fine tuning the carbon content ofa porous low-k dielectric film is another potential application.

A substrate containing a porous low-k dielectric film (e.g., CDO) orlayers of porous low-k dielectric films is submerged in a hydrogenfluoride (HF) solution. The hydrofluoric acid reacts with the porouslow-k dielectric film to yield a higher concentration of Si—OHfunctional groups in the low-k dielectric film as compared to the low-kdielectric film prior to HF exposure. The substrate may then be rinsedwith a rinsing solvent/solution and dried afterwards. After HF exposure,the substrate is then exposed to a silylation agent in the vapor orliquid phase. The silylation agent reacts with Si—OH functional groupsin the porous low-k dielectric film to increase the concentration ofcarbon in the low-k dielectric film. The substrate may be rinsed anddried if necessary. The substrate may be concurrently exposed to boththe silylation agent and UV light. The substrate may be exposed to UVlight after exposure to the silylation agent. Due to the increasedcarbon concentration, the dielectric constant of porous low-k dielectricfilm is lower than it was before HF exposure. Concentration herebyrefers to number of moles per unit volume. The HF exposure process maybe timed to control the amount of Si—OH functional groups. This controlin turn dictates the eventual carbon concentration and therefore theresulting dielectric constant.

FIG. 1A illustrates a dielectric film 100 deposited onto a structure101. The structure 101 may be a substrate, such as, for example, asilicon wafer, or a previously formed layer, such as, for example, ametallization or interconnect layer. The low-k dielectric film 100 maybe any conventional porous, low-k, silicon-based dielectric materialhaving a k-value of about 3 or less. Exemplary low-k dielectric filmsinclude, for example, SiO₂, SiOC, SiON, SiCOH, SiOCN, and other relatedfilms. In one embodiment, the low-k dielectric material is anorganosilicate glass (OSG, also known as SiCOH) which is a silicon oxidecontaining carbon and hydrogen atoms. SiCOH may have a k-value betweenabout 2 and 3 and is available as Black Diamond II™ from AppliedMaterials of Santa Clara, Calif. The low-k dielectric film 100 may havepores 102 formed therein. The pores may be nanopores. The nanopores mayhave a diameter in the range from about 0.5 nm to about 20 nm. The low-kdielectric film may be deposited by a plasma-enhanced chemical vapordeposition (PECVD) process or any other suitable deposition technique.The low-k dielectric film 100 may be a porous carbon doped oxide (CDO)film. The low-k dielectric film 100 may have a k-value greater than thek-value of the dielectric film after processing of the film.

FIG. 1B illustrates the low-k dielectric film 100 after being planarizedand etched to form features 104 into the low-k dielectric film 100. Thelow-k dielectric film 100 may be planarized by a chemical mechanicalplanarization (CMP) process, for example. The low-k dielectric film 100may be etched by masking a portion of the low-k dielectric film 100,contacting the unmasked portion of the low-k dielectric film 100 with aplasma formed from hydrofluoric acid (HF) vapor, and ashing away themask using a plasma formed from oxygen (O₂) gas or CO₂ gas, for example.The k-value of the low-k dielectric film 100 may be lowered after any ofthe processing steps using the embodiments described herein.

FIG. 1C illustrates the low-k dielectric film 100 after a diffusionbarrier 106 may be deposited into the features 104 of the low-kdielectric film 100 and a metal material 107, such as, for example,copper or a copper alloy, may be deposited into the features 104. Asillustrated in FIG. 1D, it may be necessary to planarize the metalmaterial 107 and remove any oxides from the metal material 107 that mayform during planarization. Common metal oxide removal techniques involvethe use of hydrogen or ammonia plasmas. The planarization and/or metaloxide removal processes may damage the surface of the low-k dielectricfilm 100 if the low-k dielectric film 100 has a lower k-value. As aresult, it may be desirable for the low-k dielectric film 100 to have ahigher k-value prior to and during processing than the k-value of thedielectric film 100 after the various processing steps are performed.The k-value of the dielectric film 100 may be lowered after any of theaforementioned process steps using the k-value lowering processesdescribed herein.

FIG. 2 is a process flow diagram illustrating one method 200 of loweringthe k-value of a low-k dielectric film according to embodimentsdescribed herein. At block 210, a substrate having a low-k dielectricfilm disposed thereon is positioned in a processing chamber. Thesubstrate and low-k dielectric film may be similar to the low-kdielectric film 100 and structure 101 depicted in FIGS. 1A-1D. The low-kdielectric film typically has an initial k-value which is higher thanthe final k-value of the film after performance of the method 200. Theprocessing chamber may be similar to the processing chamber 300 depictedin FIG. 3.

At block 220, the substrate may be optionally processed in-situ or in aseparate processing chamber to form features, such as vias and/ortrenches, in the low-k dielectric film using any suitable dry or wetetching process. Any masking materials and/or residues from the etchingprocess which are left on the substrate may be stripped/removed in-situor in a dedicated processing chamber using an ashing process or anyother suitable technique. Other integrations processes that may be usedto form the features include planarization processes, diffusion barrierdeposition processes, metal deposition processes, and combinationsthereof.

At block 230, the low-k dielectric film is exposed to a hydrofluoricacid (HF) solution. The hydrofluoric acid solution may be in liquid orvapor phase. The hydrofluoric acid solution may be a dilute hydrofluoric(DHF) acid solution. The hydrofluoric acid may be buffered, bufferedhydrofluoric acid (BHF), or non-buffered. Exemplary buffering agents forbuffering HF include ammonium fluoride (NH₄F). The hydrofluoric acidsolution is chosen because it is believed that the hydrofluoric acidsolution will disrupt a portion of the Si—O—Si bonding network in thelow-k dielectric film to form Si—OH bonds. The Si—OH bonds in the low-kdielectric film will allow for the insertion of additional carbon intothe low-k dielectric film resulting in a reduction of the k-value of thelow-k dielectric film. Factors such as the concentration of the dilutehydrofluoric acid solution and the time period of exposure of the low-kdielectric film to the dilute HF will affect the amount of disruption ofthe Si—O—Si network.

The low-k dielectric film may be dipped in the dilute acid solution fora period of, for example, about 30 seconds to about 800 seconds. Incertain embodiments, the dilute acid solution may be sprayed onto thelow-k dielectric film. Optionally, following exposure of the low-kdielectric film to the hydrofluoric acid solution, a post-exposure rinseprocess using for example, DI water, may be used to clean the substratesurface. The optional clean process may be followed by an optionaldrying process using drying methods known in the art.

The hydrofluoric acid solution may be a dilute solution of hydrofluoricacid (HF) in deionized water. The hydrofluoric acid solution may be fromabout 0.1% by volume to about 100% by volume hydrofluoric acid. Thehydrofluoric acid solution may be from about 1% by volume to about 70%by volume hydrofluoric acid. The hydrofluoric acid solution may includehydrofluoric acid at a concentration of about 0.1% by volume to about 5%by volume, for example, about 0.5% by volume to about 1% by volume. Thehydrofluoric acid dip may be performed at room temperature (e.g., about20° C.). The dipping time may vary depending upon the hydrofluoric acidconcentration and the amount of Si—O—Si bond disruption desired.

At block 230, the low-k dielectric film is exposed to a silylationagent. In one embodiment, the silylation process may be performed in aUV based processing chamber, such as the processing chamber 300discussed with respect to FIG. 3. The silylation process may be used torecover or repair at least some of the damage to the low-k dielectricfilm caused during block 220 as well as allowing for the insertion ofadditional carbon into the low-k dielectric film resulting in furtherreduction of the k-value of the low-k dielectric film. Exposure of theporous low-k dielectric film 100 to the silylation agent may convert theSi—OH groups in the dielectric film 100 into hydrophobic groups, forexample, Si—O—Si(CH₃)₃ groups. The hydrophobic groups assist in drivingwater out of the damaged pores 103 of the dielectric film 100.

Exposure of the low-k dielectric film 100 to the silylation agent mayoccur in vapor phase or liquid phase. The vapor phase silylation processcomprises contacting the low-k dielectric film 100 with a vaporizedsilylation agent to create the Si—O—Si(CH₃)₃ groups in the low-kdielectric film 100 described above. Vaporizing the silylation agentallows the silylation agent to penetrate deeply into the low-kdielectric film 100. Exemplary silylation agents includehexamethyldisilazane (HMDS), tetramethyldisilazane (TMDS),trimethylchlorosilane (TMCS), dimethyldichlorosilane (DMDCS),methyltrichlorosilane (MTCS), trimethylmethoxysilane (TMMS)(CH₃—O—Si—(CH₃)₃), dimethyldimethoxysilane (DMDMS) ((CH₃)₂—Si—(OCH₃)₂),methyltrimethoxysilane (MTMS) ((CH₃—O)₃—Si—CH₃), phenyltrimethoxysilane(PTMOS) (C₆H₅—Si—(OCH₃)₃), phenyldimethylchlorosilane (PDMCS)(C₆H₅—Si(Cl)—(CH₃)₂), dimethylaminotrimethylsilane (DMATMS)((CH₃)₂—N—Si—(CH₃)₃), bis(dimethylamino)dimethylsilane (BDMADMS), orother compounds containing Si, H, and C. The silylation agent may takethe form of a gas or a vaporized liquid vapor.

The vapor phase silylation process may be conducted by placing the low-kdielectric film 100 into a processing chamber, vaporizing the silylationagent, and flowing the vaporized silylation agent into the processingchamber. The silylation agent may alternatively be vaporized in theprocessing chamber. The silylation agent may be introduced into theprocessing chamber through a showerhead positioned at an upper portionof the processing chamber. A carrier gas, such as He, Ar, N₂, H₂, andcombinations thereof, may be used to assist the flow of the silylationagent into the processing chamber. Additionally, a catalyst, such aswater, may be added during the vapor phase silylation process. The vaporphase silylation process may be conducted at a processing chamberpressure from about 50 mTorr to about 500 Torr, for example, from about200 mTorr to about 6 Torr. During the silylation process, the dielectricfilm may be heated to a temperature from about 100° C. to about 400° C.,for example, from about 200° C. to about 390° C. The flow rate of thesilylation agent may be between 1 sccm and 10,000 sccm, for example,from about 100 sccm to about 2,000 sccm. The flow rate of the silylationagent may be between 400 sccm and 2,000 sccm. The flow rate of thesilylation agent may be between 1 mgm and 10,000 mgm, for example, fromabout 100 mgm to about 2,000 mgm. The flow rate of the silylation agentmay be between 1,000 mgm and 2,000 mgm. The flow rate of the optionalcarrier gas may be between 1 sccm and 10,000 sccm, for example, fromabout 2,000 sccm to about 3,000 sccm. The flow rate of the optionalcarrier gas may be between 400 sccm and 2,000 sccm. The processing timefor the vapor phase silylation may be from about 1 minute to about 10minutes. The pressure within the processing chamber may be varied duringthe vapor phase silylation process. For example, the pressure may bevaried between 50 Torr and 500 Torr.

Exposing the damaged film of the low-k dielectric film to a vaporizedsilylation agent can replenish the damaged film with carbon and also addadditional carbon to the low-k dielectric film. For example, methyl orphenyl containing silylation agents can react with the Si—OH groups inthe low-k dielectric film to convert hydrophilic Si—OH groups intohydrophobic Si—O—Si bonds (e.g., Si—O—Si(CH₃)₃ groups orSi—O—Si(CH₃)₂—O—Si groups). As hydrophobic films are less likely toretain moisture than hydrophilic films, moisture cannot affect theproperties of the treated low-k dielectric film. Therefore, the k-valueof the low-k dielectric film is restored (i.e., decreased).

At block 250, the low-k dielectric film is optionally exposed to anultraviolet cure process. The low-k dielectric film may be cured in thesame processing chamber as the k-restoration process performed in block240 using UV energy from a UV unit disposed above the UV transparent gasdistribution showerhead and the UV transparent window. The UV cureprocess of block 250 may be performed prior to the process of block 240,simultaneously with the process of block 240, subsequent to the processof block 240, or any combinations of the aforementioned sequences. TheUV cure process may be conducted by placing the low-k dielectric film100 into a processing chamber and engaging a source of UV radiation tocontact the low-k dielectric film 100 with UV radiation. The UVradiation source may be a UV lamp, for example. The UV radiation sourcemay be positioned outside of the processing chamber, and the processingchamber may have a quartz window through which UV radiation may pass.The low-k dielectric film 100 may be positioned in an inert gasenvironment, such as He or Ar, for example. The processing chamber mayalso include a microwave source to heat the low-k dielectric film 100prior to or concurrently with exposing the low-k dielectric film 100with UV radiation. The UV cure process may also be conducted usingplasma to simulate UV radiation wavelengths. The plasma may be formed bycoupling RF power to a treatment gas such as He, Ar, O₂, N₂, orcombinations thereof. The plasma may be formed by a remote plasma source(RPS) and delivered to the processing chamber.

The UV cure process may be conducted at a processing chamber pressurebetween 1 Torr and 100 Torr, such as 6 Torr, a dielectric filmtemperature between 20° C. and 400° C., such as 385° C., an environmentgas flow rate between 8,000 sccm and 24,000 sccm, such as 16,000 sccm, atreatment gas flow rate between 2,000 sccm and 20,000 sccm, such as12,000 sccm, a RF power between 50 W and 1,000 W, such as 500 W, a RFpower frequency of 13.56 MHz, a processing time between 10 sec and 180sec, such as 60 sec, a UV irradiance power between 100 W/m² and 2,000W/m², such as 1,500 W/m², and UV wavelengths between 100 nm and 400 nm.The UV cure process described above advantageously repairs the damagedpores 103 in the sidewalls of the features 104.

In one embodiment, the UV cure temperature may be from about 100° C. toabout 800° C., for example about 400° C. The UV cure time may be fromabout 10 seconds to about 600 seconds. A UV cure gas may be flown to theprocessing chamber through the UV transparent gas distributionshowerhead. In one embodiment, an inert cure gas, such as helium andargon, may be flown to the processing chamber at a flow rate betweenabout 1,000 sccm to about 27,000 sccm.

In another embodiment, the silylation process in block 240 and UV curingin block 250 can be performed simultaneously. In such a case, the UVunit turns on/off at the same time with the silylation process. Inanother embodiment, the UV cure in block 250 may be performed before thesilylation process in block 240. In yet another embodiment, thesilylation process in block 240 and the UV cure in block 250 can beperformed alternately. For example, the UV cure may be performed toremove some water from surface/side wall. The silylation is thenperformed to recover surface hydrophobicity. The UV cure is thenperformed to further recover low-k film damage. In such a case, thesilylation and the UV cure may be performed for about 15 to about 30seconds, respectively. It is contemplated that the silylation agent flowrate, time, UV power, substrate temperature, chamber pressure ofsilylation and UV cure process may vary depending upon the application.If desired, the UV curing may be performed in a separate processingchamber different than the processing chamber for the silylationprocess.

Various purge gas and evacuation processes may be performed duringmethod 200. For example, it may be advantageous to evacuate the chamberafter insertion of the low-k dielectric film into the processing chamberprior to the silylation process of block 240. The processing chamber maybe evacuated by use of vacuum pump.

After performance of method 200, the substrate with the low-k dielectricfilm disposed thereon may be removed from the processing chamber andexposed to a rinsing solvent/solution followed by an optional dryingprocess.

FIG. 3 is a cross-sectional view of an exemplary processing chamber thatmay be used to practice the embodiments described herein. FIG. 3 isbased upon features of the PRODUCER® chambers currently manufactured byApplied Materials, Inc. The PRODUCER CVD chamber (200 mm or 300 mm) hastwo isolated processing regions that may be used to deposit carbon-dopedsilicon oxides and other materials.

FIG. 3 illustrates a tandem processing chamber 300 that is configuredfor UV curing. The tandem process chamber 300 includes a body 301 and alid 303 that can be hinged to the body 301. Coupled to the lid 303 aretwo housings 305 that are each coupled to inlets along with outlets forpassing cooling air through an interior of the housings 305. The coolingair can be at room temperature or approximately twenty-two degreesCelsius. A central pressurized air source (not shown) provides asufficient flow rate of air to the inlets to insure proper operation ofany UV lamp bulbs and/or power sources 313 for the bulbs associated withthe tandem process chamber 300.

FIG. 3 shows a partial section view of the tandem process chamber 300with the lid 303, the housings 305 and the power sources 313 that isconfigured for UV curing. Each of the housings 305 cover a respectiveone of two UV lamp bulbs 302 disposed respectively above two processregions 320 defined within the body 301. Each of the process regions 320includes a heating pedestal 306 for supporting a substrate 308 withinthe process regions 320. The pedestals 306 can be made from ceramic ormetal such as aluminum. Preferably, the pedestals 306 couple to stems310 that extend through a bottom of the body 301 and are operated bydrive systems 312 to move the pedestals 306 in the processing regions320 toward and away from the UV lamp bulbs 302. The drive systems 312can also rotate and/or translate the pedestals 306 during curing tofurther enhance uniformity of substrate illumination. Adjustablepositioning of the pedestals 306 enables control of volatile cureby-product and purge and clean gas flow patterns and residence times inaddition to potential fine tuning of incident UV irradiance levels onthe substrate 308 depending on the nature of the light delivery systemdesign considerations such as focal length.

In general, embodiments of the invention contemplate any UV source suchas mercury microwave arc lamps, pulsed xenon flash lamps orhigh-efficiency UV light emitting diode arrays. The UV lamp bulbs 302are sealed plasma bulbs filled with one or more gases such as xenon (Xe)or mercury (Hg) for excitation by the power sources 313. Preferably, thepower sources 313 are microwave generators that can include one or moremagnetrons (not shown) and one or more transformers (not shown) toenergize filaments of the magnetrons. In one embodiment having kilowattmicrowave (MW) power sources, each of the housings 305 includes anaperture 315 adjacent the power sources 313 to receive up to about 6,000W of microwave power from the power sources 313 to subsequently generateup to about 100 W of UV light from each of the bulbs 302. In anotherembodiment, the UV lamp bulbs 302 can include an electrode or filamenttherein such that the power sources 313 represent circuitry and/orcurrent supplies, such as direct current (DC) or pulsed DC, to theelectrode.

The power sources 313 for some embodiments can include radio frequency(RF) energy sources that are capable of excitation of the gases withinthe UV lamp bulbs 302. The configuration of the RF excitation in thebulb can be capacitive or inductive. An inductively coupled plasma (ICP)bulb can be used to efficiently increase bulb brilliancy by generationof denser plasma than with the capacitively coupled discharge. Inaddition, the ICP lamp eliminates degradation in UV output due toelectrode degradation resulting in a longer-life bulb for enhancedsystem productivity. Benefits of the power sources 313 being RF energysources include an increase in efficiency.

Preferably, the bulbs 302 emit light across a broad band of wavelengthsfrom 170 nm to 400 nm. The gases selected for use within the bulbs 302can determine the wavelengths emitted. Since shorter wavelengths tend togenerate ozone when oxygen is present, UV light emitted by the bulbs 302can be tuned to predominantly generate broadband UV light above 200 nmto avoid ozone generation during cure processes.

UV light emitted from the UV lamp bulbs 302 enters the processingregions 320 by passing through windows 314 disposed in apertures in thelid 303. The windows 314 preferably are made of an OH free syntheticquartz glass and have sufficient thickness to maintain vacuum withoutcracking. Further, the windows 314 are preferably fused silica thattransmits UV light down to approximately 150 nm. Since the lid 303 sealsto the body 301 and the windows 314 are sealed to the lid 303, theprocessing regions 320 provide volumes capable of maintaining pressuresfrom approximately 1 Torr to approximately 650 Torr. Processing orcleaning gases 317 enter the process regions 320 via a respective one oftwo inlet passages 316. The processing or cleaning gases 317 then exitthe process regions 320 via a common outlet port 318. Additionally, thecooling air supplied to the interior of the housings 305 circulates pastthe bulbs 302, but is isolated from the process regions 320 by thewindows 314.

EXAMPLES

Objects and advantages of the embodiments described herein are furtherillustrated by the following examples. The particular materials andamounts thereof, as well as other conditions and details, recited inthese examples should not be used to limit the embodiments describedherein.

For sample 1 and sample 2 the wafers were transferred between processingchambers without breaking vacuum. For the repair process performed insample 1 and sample 2 there were two process steps. For the firstprocess UV was not applied. UV was applied during the second process.Although samples 1 and 2 were performed in separate chambers a singlechamber may be used with simultaneous chemical and UV exposure.

Sample 1:

A Black Diamond II™ low-k dielectric film was dipped in an etchantsolution (1:100 hydrofluoric acid: water) for one minute to inducedamage within the low-k dielectric film. The damaged low-k dielectricfilm was rinsed with DI water to remove excess hydrofluoric acid anddried. The damaged low-k dielectric film was positioned in a PRODUCERCVD processing chamber. The low-k dielectric film was heated to about385° C. The pressure in the processing chamber was adjusted to about 6Torr. Dimethylaminotrimethylsilane (DMATMS) along with a helium carriergas was flown into the processing chamber. The flow rate of the DMATMSand the helium carrier gas was about 1,000 mgm and 2,000 sccmrespectively. The processing time for the vapor phase silylation wasabout three minutes.

After the silylation process, the low-k dielectric film was transferredto a second processing chamber for UV exposure. The low-k dielectricfilm was heated to about 385° C. The pressure in the processing chamberwas adjusted to about 6 Torr. Helium gas and argon gas were flown intothe processing chamber. The flow rate of helium gas and argon gas wasabout 16,000 sccm and about 16,000 sccm respectively. The UV exposuretime was about 30 seconds with about 95% of UV output and UV wavelengthsbetween 100 nm and 400 nm.

Sample 2:

A Black Diamond II™ low-k dielectric film was dipped in etchant solution(1:100 hydrofluoric acid:water or diluted HF “DHF”) for five minutes toinduce damage within the low-k dielectric film. The damaged low-kdielectric film was rinsed with DI water to remove excess hydrofluoricacid and dried. The damaged low-k dielectric film was positioned in aPRODUCER CVD processing chamber. The low-k dielectric film was heated toabout 385° C. The pressure in the processing chamber was adjusted toabout 6 Torr. Dimethylaminotrimethylsilane (DMATMS) along with a heliumcarrier gas was flown into the processing chamber. The flow rate of theDMATMS and the helium carrier gas was about 1,000 mgm and 2,000 sccmrespectively. The processing time for the vapor phase silylation wasabout three minutes.

After the silylation process, the low-k dielectric film was transferredto a second processing chamber for UV exposure. The low-k dielectricfilm was heated to about 385° C. The pressure in the processing chamberwas adjusted to about 6 Torr. Helium gas and argon gas were flown intothe processing chamber. The flow rate of helium gas and argon gas wasabout 16,000 sccm and about 16,000 sccm respectively. The UV exposuretime was about 30 seconds with about 95% of UV output and UV wavelengthsbetween 100 nm and 400 nm.

Sample 3:

A Black Diamond II™ low-k dielectric film was dipped in etchant solution(1:100 hydrofluoric acid:water or diluted HF “DHF”) for ten minutes toinduce damage within the low-k dielectric film. The damaged low-kdielectric film was rinsed with DI water to remove excess hydrofluoricacid and dried. The damaged low-k dielectric film was positioned in aPRODUCER CVD processing chamber. The low-k dielectric film was heated toabout 385° C. The pressure in the processing chamber was adjusted toabout 6 Torr. Dimethylaminotrimethylsilane (DMATMS) along with a heliumcarrier gas was flown into the processing chamber. The flow rate of theDMATMS and the helium carrier gas was about 1,000 mgm and 2,000 sccmrespectively. The processing time for the vapor phase silylation wasabout three minutes.

Sample 3 was not exposed to UV since the film was destroyed duringexposure to the etchant solution.

Results:

TABLE 1 Etch Time Before HF After HF After Repair Sample (min.) Thick RIk-avg. Thick. RI k-avg. Thick. RI k-avg. 1 1 1,972 1.3437 2.54 1,9711.3456 2.61 1907 1.3596 2.41 2 5 1,992 1.3427 2.54 2084 1.3050 2.87 18701.3586 2.24 3 10 1,990 1.3430 2.54 20 1.1079 n/a

As depicted in Table 1, Sample 2 (5-minute DHF exposure) had a higherk-value than Sample 1 (1-minute DHF exposure) after HF exposure. Thusthe DHF exposure time trended with post-DHF k-value. Not to be bound bytheory but it is believed that increased exposure time of Sample 2 toDHF yielded more damage (e.g., Si—OH). Due to the increased damage inSample 2, Sample 2 had a lower k after silylation.

Single beam measurements of the films post-damage and post-repair wereperformed. Subtraction of one single-beam spectrum from the other yieldsa difference spectrum that shows intensity gains and losses at variouswavenumbers. A comparison of FTIR difference spectra (repaired minusdamaged) demonstrated that Sample 2 had a larger increase in carbon andSi—O—Si and a larger decrease in Si—OH during silylation. All of theseoutcomes are results of having more SiOH after DHF exposure(SiOH+DMATMS→Si—O—Si-Me₃+DMA). FTIR analysis is a measure of the numberof reactions and the presence of more Si—OH indicates more reactions.Dimethylamine (DMA) is a by-product of the reaction of DMATMS withSi—OH.

Using certain embodiments described herein, the dielectric constant of alow-k dielectric film was reduced from low-k dielectric film having a kof 2.54 into a low-k dielectric film having a k of 2.24. In order toreduce the dielectric constant of a low-k film, we have to damage tolarger extent (the intermediate k-value between DHF exposure andexposure to the silylation agent has to be higher). The DHF processtherefore controls the outcome. However, if the DHF exposure time is toolong, the low-k dielectric film may be destroyed as shown by Sample 3which was exposed for a time period of ten minutes. In addition to time,other factors such as temperature and concentration will dictate if theprocess is viable and how low the dielectric constant of the final filmis.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for lowering a dielectric constant (k) of a low-ksilicon-containing dielectric film, comprising: exposing a low-ksilicon-containing dielectric film to a hydrofluoric acid solution; andsubsequently exposing the low-k silicon-containing dielectric film to asilylation agent.
 2. The method of claim 1, wherein the low-ksilicon-containing dielectric film has a lower dielectric constant (k)after exposure to the silylation agent as compared to the dielectricconstant (k) of the low-k silicon containing dielectric prior toexposure to the hydrofluoric acid solution.
 3. The method of claim 1,wherein the low-k silicon-containing dielectric film is a silicon baseddielectric material having an initial dielectric constant of three orless.
 4. The method of claim 3, wherein the low-k silicon-containingdielectric film is a silicon oxide containing carbon and hydrogen. 5.The method of claim 1, wherein the low-k silicon-containing dielectricfilm is exposed to an integration process selected from: a planarizationprocess, an etching process, a diffusion barrier deposition process, ametal deposition process, and combinations thereof prior to exposing thelow-k silicon-containing dielectric film to a hydrofluoric acidsolution.
 6. The method of claim 1, wherein the hydrofluoric acidsolution disrupts a portion of the Si—O—Si bonding network of the low-ksilicon-containing dielectric film to form Si—OH functional groups. 7.The method of claim 6, wherein the silylation agent reacts with Si—OHfunctional groups in the low-k silicon-containing dielectric film toincrease the concentration of carbon in the low-k silicon-containingdielectric film.
 8. The method of claim 1, further comprising exposingthe low-k silicon-containing dielectric film to an ultraviolet cureprocess.
 9. The method of claim 8, wherein exposing the low-ksilicon-containing dielectric film to an ultraviolet cure process isperformed prior to exposing the low-k silicon-containing dielectric filmto a silylation agent, simultaneously with exposing the low-ksilicon-containing dielectric film to a silylation agent, subsequent toexposing the low-k silicon-containing dielectric film to a silylationagent, or combinations thereof.
 10. The method of claim 9, whereinexposing the low-k silicon-containing dielectric film to an ultravioletcure process is performed subsequent to exposing the low-ksilicon-containing dielectric film to a silylation agent.
 11. The methodof claim 1, wherein the silylation agent is in vapor phase and isselected from the group consisting of: hexamethyldisilazane (HMDS),tetramethyldisilazane (TMDS), trimethylchlorosilane (TMCS),dimethyldichlorosilane (DMDCS), methyltrichlorosilane (MTCS),trimethylmethoxysilane (TMMS) (CH₃—O—Si—(CH₃)₃), dimethyldimethoxysilane(DMDMS) ((CH₃)₂—Si—(OCH₃)₂), methyltrimethoxysilane (MTMS)((CH₃—O)₃—Si—CH₃), phenyltrimethoxysilane (PTMOS) (C₆H₅—Si—(OCH₃)₃),phenyldimethylchlorosilane (PDMCS) (C₆H₅—Si(Cl)—(CH₃)₂),dimethylaminotrimethylsilane (DMATMS) ((CH₃)₂—N—Si—(CH₃)₃),bis(dimethylamino)dimethylsilane (BDMADMS), and combinations thereof.12. The method of claim 11, wherein the silylation agent is DMATMS. 13.A method for lowering a dielectric constant (k) of a low-ksilicon-containing dielectric film, comprising: exposing a low-ksilicon-containing dielectric film to a hydrofluoric acid solution;exposing the low-k silicon-containing dielectric film to a vaporizedsilylation agent; and exposing the low-k silicon-containing dielectricfilm to an ultraviolet (UV) cure process.
 14. The method of claim 13,wherein exposing a low-k silicon-containing dielectric film to avaporized silylation agent and exposing a low-k silicon-containingdielectric film to an ultraviolet cure process are performed in the sameprocessing chamber.
 15. The method of claim 13, wherein the UV cureprocess is performed at a UV cure temperature from about 100 degreesCelsius to about 800 degrees Celsius.
 16. The method of claim 15,further comprising using a plasma to simulate UV radiation wavelengths.17. The method of claim 16, wherein the plasma is formed by a remoteplasma source.
 18. The method of claim 13, wherein exposing the low-ksilicon-containing dielectric film to a vaporized silylation agent andexposing the low-k silicon-containing dielectric film to a UV cureprocess are performed simultaneously.
 19. The method of claim 13,further comprising: repeating the exposing the low-k silicon-containingdielectric film to a vaporized silylation agent and the exposing thelow-k silicon-containing dielectric film to a UV cure process.